The present invention relates to an elastic strut having an integrated weight/spring type resonator employed in particular, but not exclusively, in bar suspension systems for the main transmission on the structure of the fuselage of rotary wing aircraft for filtering the vibrations produced by the lifting rotor of these aircraft.
These suspension systems are well known and comprise a connection between the main transmission box and the fuselage, constituted by an assembly of rigid bars forming a pylon each of which are connected to the fuselage of the aircraft through an elastic device and, as the case may be, an associated resonator for filtering the longitudinal, lateral and vertical dynamic excitations coming from the head of the rotor.
FR-2 450 200 discloses a suspension device in which rigid elements of the system, or pylon, are connected to the structure of the fuselage by elastic studs of elastomer operating in shear stress, and thereby introducing an axial elasticity characteristic. However, this device does not comprise a resonator element necessary for obtaining a high degree of attenuation of the vibrations between the rotor and the fuselage.
EP-A-0 015 378 discloses an elastic device associated with a resonator including the application of the "liquid lever" principle, i.e. a mechanism in which a liquid of low viscosity acts as a lever on a shaft and a weight connected to a spring. This liquid of low viscosity, contained within a volume which is variable by means of two corrugated metal membranes which seal the system, is put under pressure by a spring. The axial beating weight is in this way put into alternating motion by the variations in the pressure of the liquid which themselves result from provoked variations of the volume of the container of said liquid. The resonator is axially guided by ball bearings.
On one hand, this type of resonator is particularly expensive to manufacture as concerns the metal membranes; on the other hand, it is very difficult to achieve good reliability of these membranes owing to the fact that, in operation, they are subjected to large dynamic stresses and any fatigue crack which occurs therein results in a leakage of liquid and consequently a total loss of the effectiveness of the resonator.
Furthermore, in known resonators, it has been found necessary, in order to limit the size of the weight, to amplify its displacement by mechanical lever systems. The maximum ratio of the amplification thus obtained is limited to about 8 owing to technological requirements.